Bumble Bee

The common name of bumble bee possibly comes from their rather large, clumsy appearance and/or the buzzing sound they make as they fly. Bumble bees usually nest in cavities below ground (often abandoned rodent burrows), but often will use brush piles, trash heaps and occasionally bird houses as nesting sites. They become a concern because of their abundance around the many flowering plants typical of yards, and their often very painful sting. There are about 51 species in the United States and Canada, with 6 or 8 in the greater Kansas City area.

Recognition

The adult worker body length is about ½ -1”; queens are about ¾-1” long and both are robust in form. As most, but not all bees, they have two wings.Their color is black with yellow (rarely orange) markings, an overall fuzzy appearance, including the top surface of abdomen. The fuzzy top surface of the abdomen immediately differentiates them from carpenter bees. Stinger relatively smooth, with small barbs.

Similar Groups

Carpenter bees (Xylocopa spp.) with top surface of abdomen largely bare and shining.

Some robber flies (Diptera: Asilidae) which have only 1 pair of wings.

Some hawk moths (Lepidoptera: Sphingidae) have siphoning mouthparts.

Biology

Bumble bees are social insects which live in nests or colonies. The adults are represented by workers (Psithyrus spp.lack workers) which are sterile females, queens, and males (drones) which come from unfertilized eggs and usually appear in late summer. Typically, only inseminated queens overwinter and do so underground. In the spring, the queens of Psithyrus species wait until the Bombus nests are moderate in size and then parasitize them. The Bombus queens select a suitable subterranean cavity or surface grass clump as a nesting site. Then the Bombus queen fashions a honey pot of wax scales near the nest entrance into which she regurgitates nectar. Next she makes a pollen clump on the nest floor and lays 8-10 eggs on it. The queen will periodically add pollen and nectar to the peripheral edges of the clump, and eventually more eggs.

Their developmental time (egg to adult) is 16-25 days, with 4 larval molts. Workers live about 2 weeks. Most first brood workers are small due to nutrition. The queen will increase the number of eggs laid as the number of workers to care for them increases.

During the summer, parasitism may eliminate up to 50% of the colony’s workers each week. However, a mature bumble bee nest ultimately contains about 50-400 bees at any given time; the largest known nest contained 756 bees and 385 brood (larvae and pupae).

The nest temperature is regulated to about 86° F (30° C). This thermoregulation is accomplished by the bee relaxing the 3rd axillary muscle to its wings which unhinges the wings from the main power-producing thoracic muscles. Then contractions of these large muscles produces body heat without wing movement.

In the late summer only males (drones) and new queens are reared in the nest. Once these new queens emerge, they mate and find a suitable place to overwinter. The males, workers, old queen, and any virgin new queens die with the onset of cold weather.

Habits

Depending on the Bombus species, the overwintering queen will select an appropriate nesting site the following spring. The queen of some Bombus species locate a dark cavity at least ¾ inch high by 1 1/8 inch wide containing fine plant fiber; such a nest is usually underground and often an abandoned mouse nest. Queens of other Bombus species select a dense clump of grass on the surface for a nest, adding grass on top. The queens of Psithyrus species are all parasitic on Bombus nests are moderate in size and can therefore support them. They then enter the nest, kill the Bombus queen, and take over the nest using the Bombus workers to care for her young. Bombus queens of later emerging Bombus species sometimes also parasitize the nests of earlier emerging Bombus species.

Depending on the Bombus species, the overwintering queen will select an appropriate nesting site the following spring. The queen of some Bombus species locate a dark cavity at least ¾ inch high by 1 1/8 inch wide containing fine plant fiber; such a nest is usually underground and often an abandoned mouse nest. Queens of other Bombus species select a dense clump of grass on the surface for a nest, adding grass on top. The queens of Psithyrus species are all parasitic on Bombus nests are moderate in size and can therefore support them. They then enter the nest, kill the Bombus queen, and take over the nest using the Bombus workers to care for her young. Bombus queens of later emerging Bombus species sometimes also parasitize the nests of earlier emerging Bombus species.

Defense is usually done by using their relatively smooth stingers which can be used over and over. Some species will also spray feces, and some cover the intruder with regurgitated honey. People sensitive to insect venom should always exercise care around bumble bee nests.

Control

While bumble bees are considered beneficial insects as pollinators, if their nest is located in or close to an occupied structure or recreational area, then control may warranted. During the day, find the location of each nest by observing where the bees disappear into the ground, grass clump, or structure. At night using background light and while wearing a bee veil, apply an appropriately labelled pyrethroid pesticide. Dusts work best when applied to an area 6” (15 cm) around the nest entrance. For structural nests, treat with dust or aerosol but do not seal the entrance. Once treated, the nest site should be opened up and cleaned out within 1-2 days to prevent future problems with dermestid beetles, spider beetles, and/or psocids.